Ashli Walker rifled through a rack of designer T-shirts one recent afternoon, pondering which one she should buy and wear the next day to Eleanor Roosevelt High School in Prince George's County. The big black one that read, "TRUST ME..I'M SINGLE"? Or the snug white T-shirt emblazoned with, "I KNOW WHAT BOYS WANT"?

They're blatantly sexual, occasionally clever and often loaded with double meanings, forcing school administrators and other students to read provocations stripped across the chest, such as "yes, but not with u!," "Your Boyfriend Is a Good Kisser" and "two boys for every girl." Such T-shirts also are emblematic of the kind of sleazy-chic culture some teenagers now inhabit, in which status can be defined by images of sexual promiscuity that previous generations might have considered unhip.

The T-shirts, which school officials say are racier than ever, are posing dress-code dilemmas on Washington area campuses. School systems typically ban clothing that expresses vulgarity, obscenity or lewdness or that promotes cigarettes, alcohol, drugs or weapons. For instance, T-shirts advertising Budweiser or the movie "Scarface," with Al Pacino holding a tommy gun, are taboo.

But sexually suggestive T-shirts often fall into a gray area that requires officials to evaluate one shirt at a time. Some messages are considered harmless -- "Single and Ready to Mingle" or "My Boyfriend Is a Good Kisser." Others are not.

"We try not to make a huge deal out of it, but we also want to be protecting the school environment," said Rick Mondloch, an associate principal at Robinson Secondary School in Fairfax County, who recently ordered a "Pimps" shirt turned inside out. "These shirts are more risque than they were even five years ago and probably a little more blunt, so you have to be attuned to it."

Robynne Prince, an assistant principal at Eleanor Roosevelt, said: "If there are shirts with obvious sexual connotations, then we know exactly what we're going to do, but there are some students who push the envelope."

For teenagers who chafe at clothing rules for midriffs and cleavage, "attitude" shirts offer a chance to show some skin, without showing skin.

"We have so many dress codes or whatever, so the T-shirts are like us rebelling against the teachers and principals because we can't wear what we want," said Ashli, 17, a junior at Eleanor Roosevelt, in Greenbelt, who said she does not want to have sex until she is married. "I think most girls and boys get the T-shirts because they're funny and they draw attention to you. I don't really care what guys say."

Her mother, Yakini Ajanaku, does not mind her daughter's T-shirts because she said Ashli wears them to be ironic. "I know she's a sweet girl, and I know that she's very conservative and is not sexually active," Ajanaku said. "Other people would probably get the wrong message, but I am pretty much like, 'Who cares what they think?' "

In a culture that bombards teenagers with sexual imagery -- think of rapper 50 Cent's song "Candy Shop," about the pleasures of consuming lollipops -- the T-shirts are just another way to revel in raunchy entertainment, without necessarily getting physical, according to students interviewed for this story.

"It gives me a little edge, but it's just to get a rise out of people, because people know me," said Allison Wynn, 17, a senior at Osbourn Park High School in Prince William County. "They're just like in every ad you see in magazines, people wearing these clothes or they're always making out. It's how you want to be. My boyfriend thinks it's funny." She said she is fond of wearing a shirt that says, "Don't Call Me a Cowgirl Until You See Me Ride."

Joanne Wynn said her daughter's shirts are humorous. "If it's not in good taste, I don't let [her] wear it," she said.

The T-shirts highlight a paradox about this generation: Even as more teenagers absorb ubiquitous sexual messages, federal data show that they report having less sex than their predecessors.

Although a recent National Center for Health Statistics survey found that more than half of all teenagers engage in oral sex, teen pregnancy rates have plummeted since the early 1990s. According to the Centers for Disease Control and Prevention, the percentage of high school students who reported having sexual intercourse dropped from 54 percent in 1991 to 47 percent in 2005.

"It's a puzzling picture," said Sarah Brown, director of the National Campaign to Prevent Teen Pregnancy in the District. "When someone sees a girl or boy in provocative clothing, they make a lot of assumptions about what's going on, which may or may not be true -- which really is the point, isn't it?"

Suggestive T-shirts have been around for years. A decade ago, some teenagers sported shirts that featured Coed Naked sporting events or Mr. Zog's Sex Wax. But school officials now are dealing with shirts that are much more blunt. It's up to them to determine what's innocuous, what's mildly suggestive and what, frankly, is truly awful.

At Potomac Senior High School in Prince William, a girl recently wore a black T-shirt parodying the "Got Milk?" ad, with sexual slang replacing the word "milk." Steve Bryson, the school's administrative assistant, brought the girl into his office. "I asked her, 'Why would you wear something like that?' And she said: 'I don't know. My dad knows that I have it,'" he recalled. "So I called the dad, and, of course, he had no idea. He said, 'Throw it away.' "

One popular merchant of suggestive shirts is Hollister Co., a chain owned by Abercrombie & Fitch. Its shirts say such things as "two boys for every girl" and "FLIRTING MY WAY TO THE TOP."

Asked about the messages his company markets to teenagers, Thomas D. Lennox, Abercrombie & Fitch's vice president of corporate communications, said, "Our T-shirts are sometimes controversial, which we're fine with." He declined to elaborate.

When students are caught with shirts that cross the line, they are usually given a school T-shirt or asked to turn theirs inside out. Administrators said evaluating the shirts can be awkward because the words are usually printed right over a student's chest. Sometimes students stride quickly past or take other evasive maneuvers to conceal a questionable T-shirt.

"It's almost like a live-action Pac-Man game. You see them coming through the hall, and they're trying to avoid you," said Myca Gray, an assistant principal at Gar-Field Senior High School in Prince William.

At Eleanor Roosevelt, students caught with over-the-line shirts sometimes must wear school shirts that mark them as "dress code violators." One day, Assistant Principal LaTanya Catron saw sophomore Paula Akanni wearing a tight black T-shirt that said, "I AM TOO HOT TO HANDLE." The word "Hot" had gold studs on the letters.

"Are you too hot to handle?" Catron asked with a smile. "Is that for the boys?

"It's for nobody," Akanni replied, walking away.

Most parents interviewed said that they would rather not see their kids wear the racy shirts but that they sometimes give in. Rosa Pulley tried to order her daughter Keana, 17, a Gar-Field senior, to return a T-shirt that says, "yes, but not with u!" But Keana insisted. "I have to pick my battles," the mother said. "Okay, I don't like it. She's wearing it, but it could be something worse."

Keana said her shirt's message was ambiguous. "It could mean, 'Yes, I want to go to the movies, but not with you,' " she said. "If I wanted to be sexy, like on MTV, I would just buy low-cut tight shirts."

The T-shirt trend appears to have no racial or ethnic boundaries. Girls appear to wear them more often. Guys say there is nothing confusing about the messages. "When I see a T-shirt that says, '100% single,' then you're compelled to go up and talk to them," said Paul Barrett, 17, a senior at Osbourn Park. "But if they're not single, it'd kind of [tick] me off, like they're a tease. I wouldn't let my girlfriend wear that."

At the boutique in Prince George's, Ashli decided what she would wear to school. Back to the rack went "TRUST ME..I'M SINGLE." She took "I KNOW WHAT BOYS WANT" and headed the register.